The boys and girls of the Mozilla project have taken the wraps off the beta for Prism 1.0. Prism is a technology which blurs the boundaries between the web and the desktop, allowing you to approach web sites as if they were ordinary desktop applications. Prism is cross-platform, and runs on Linux, Mac OS X, and Windows.

If the websites look at all "app-liked" rather than "website-like," to do even what you describe you need some kind of HTTP-based control protocol (e.g., SOAP) and a portable runtime (in this case, XUL).

So with all this infrastructure, you might as well do more than simply having smart links and a few custom settings!

But they're not app-like, they're just websites in their own frame with some extra Firefox JS API for interfacing with some desktop functionality. This has nothing to do with XUL except that it uses xulrunner as essentially a low overhead container for Gecko.

You can of course create apps in XUL + JS, but that's not what this is.